A projectile barrier and method is described in US 2007/0009694. An elastomeric bonding layer is spray-coated on the outside surface of a fuel tank. A composite expansion layer is then spray-coated on the bonding layer. Finally, a compression layer is spray-formed to the desired thickness on the outside of the expansion layer. When a bullet penetrates the fuel tank wall, the expansion layer comes into contact with the fuel and expands to fill the bullet hole. Whilst being suitable for providing protection against a small projectile such as a bullet, the barrier is less effective against a larger projectile. Also, the barrier is only effective in protecting a fuel tank wall. Also, the spray-coating process requires the elastomer to dissolve in a solvent, and so only relatively low molecular weight elastomers can be used.
WO 2004/098993 describes an aircraft wing with a leading edge containing a foam or honeycomb material which absorbs the impact of a bird strike.